Knee prosthesis

ABSTRACT

A knee prosthesis for use in a total knee replacement surgical procedure may include a femoral component, a tibial component and a meniscal component. Optionally, the prosthesis may also include a patellar component. The femoral component may include a bone attachment side and a joint facing side, the latter including an anterior joint surface, a posterior joint surface having a cross-sectional shape defining a portion of a cylinder, and medial and lateral grooves between the anterior and posterior joint surfaces. The meniscal component may include a number of features designed to mate with the femoral component to provide relatively natural movement and range of motion about the knee joint as well as stability and resistance to wear and tear.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention is related to surgical devices for total knee replacementsurgery. More specifically, the invention is related to a kneeprosthesis for total knee replacement surgery.

2. Description of the Related Art

Approximately 581,000 total knee replacement surgeries (also referred toas total knee arthroplasty (“TKA”)) are performed annually in the U.S.for the treatment of chronic knee pain and dysfunction. As the U.S. andworld populations become older and more obese and knee joints enduregreater wear and tear from increased loads and years of stress, TKAbecomes a more and more commonly performed surgical procedure. The goalsof TKA are to provide the patient with a knee joint that is pain free,moves naturally through a full range of motion, provides stabilityduring motion and rest, and lasts as long as possible. Many differenttotal knee implants (or “knee prostheses”) have been developed inpursuit of these goals, but no total knee prosthesis is perfect. Someknee prostheses, for example, sacrifice some amount of stability inorder to provide greater range of motion, while other prostheses do justthe opposite. Other prostheses may provide certain kinematic advantagesbut may wear out more easily, thus requiring revision surgery morefrequently. Although much of the success of TKA procedures can beattributed to surgeon skill and experience, rather than the prosthesesthemselves, improvements in total knee prostheses are still beingsought.

The knee joint is generally defined as the point of articulation of thefemur with the tibia. Structures that make up the knee include thedistal femur, the proximal tibia, the patella, and the soft tissueswithin and surrounding the knee joint. Four ligaments are especiallyimportant in the functioning of the knee—the anterior cruciate ligament,the posterior cruciate ligament, the medial collateral ligament, and thelateral collateral ligament. In an arthritic knee, protective cartilageat the point of articulation of the femur with the tibia has been wornaway, which causes significant pain and discomfort. In a TKA procedure,the distal end of the femur, the proximal end of the tibia, and oftenthe inner surface of the patella are replaced with prosthetic parts toprovide smooth, well-aligned surfaces for joint movement, while alsocreating a stable knee joint that moves through a wide range of motion.

A typical knee prosthesis includes a femoral component, a tibial tray orplateau and a tibial bearing insert (or “meniscal component”) coupled tothe tibial tray. The prosthesis may also include a patellar component,if replacing that bone surface is necessary. The femoral componentgenerally includes a pair of laterally spaced apart condylar portionsthat have distal surfaces that articulate with complementary condylarelements formed in a tibial bearing insert.

As mentioned above, the TKA procedure and total knee prosthesesgenerally try to achieve several basic goals: (1) Painreduction/elimination; (2) Natural and full range of motion about theknee joint; (3) Joint stability; (4) Correctly sized and implanted jointto minimize wear and tear of the prosthesis; and (5) Preservation of asmuch of the patient's existing bone and soft tissue (ligaments andtendons) as possible. The goals of freedom of motion and stability canconflict with one another, since creating a more stable knee joint oftenmeans reducing freedom of motion. In trying to achieve these variousgoals, three categories of total knee prostheses/procedures have beendeveloped.

In a knee joint resurfacing procedure, the articular surface of thedistal femur and proximal tibia are “resurfaced” with respectivecondylar-type articular bearing components. These knee prosthesesprovide substantial rotational and translational freedom and requireminimal bone resection to accommodate the components in the availablejoint space. The patellofemoral joint may also be resurfaced by a thirdprosthetic component. The femoral, tibial and patellar prostheticresurfacing components are affixed to respective adjacent bone structureby a cementing or by a biological bone ingrowth fixation means or anyother suitable technique.

In a second type of TKA, a mechanically linked or hinged knee prosthesisprovides a fixed fulcrum flexion-extension capability. The hinged knee,therefore, is usually surgically indicated in selected cases where thesurrounding soft tissue structures are grossly degenerated and incapableof providing functionally acceptable knee joint stability.

The third category of total knee prosthesis, the posterior stabilizedtotal knee, provides more predictable kinematics than the firstcategory. The posterior stabilized total knee prostheses essentiallyincorporate all of the functional features of the first category, thatis, the resurfacing condylar-type of knee prostheses, in addition toincorporating a mechanical cam/follower mechanism for providingposterior (tibia-to-femur) constraint. The cam/follower mechanism ispositioned within the intercondylar space of the femoral component andprovides substitutional posterior constraint to compensate for lostanterior and/or posterior cruciate ligament function or for compromisedposterior knee stability. This cam/follower mechanism enables the femurto roll back on the tibia, providing a mechanical advantage to thequadriceps during flexion.

Although many different posterior stabilized total knee prostheses havebeen developed and some work well, there is still much room forimprovement. For example, most currently available prostheses compromiseeither knee joint stability or natural, full range of motion to anextent that is suboptimal for a patient. Additionally, most prostheseswear out more quickly than would be ideal, often in predictable wearpatterns. Another limitation with conventional posterior cruciatesubstituting knee designs is that they require excess removal of bonefor implantation. Excessive bone removal can lead to intraoperativefractures due to the stress concentration created by cutting out bone toaccommodate the box of the design. Bone removal is also disadvantageous,because, in the event of revision surgery, the more bone available, theeasier the revision surgery will be.

Therefore, a need exists for an improved knee prosthesis for a totalknee arthroplasty procedure. Ideally, an improved prosthesis wouldprovide natural kinematics, full range of motion through the knee joint,as well as a stable feeling joint. Also ideally, the knee prosthesiswould have improved wear characteristics compared with most currentlyavailable prostheses. At least some of these objectives will be met byvarious embodiments of present invention.

SUMMARY OF THE INVENTION

The present invention provides an improved knee prosthesis for totalknee arthroplasty. The prosthesis may have a number of advantages, suchas but not limited to effectively replicating natural knee kinematicsand reducing wear and tear of the prosthesis thus prolonging its usefullife in situ. In various embodiments, the prosthesis may be provided asa system including multiple components, such as a femoral component,tibial component, meniscal component and patellar component, or somesubset of those components.

In one aspect of the invention, a knee prosthesis for use in a totalknee replacement surgical procedure may include a femoral component, atibial component and a meniscal component. The femoral component mayinclude a bone attachment side for attaching to a cut distal end of afemur and a joint facing side opposite the bone attachment side. Thejoint facing side of the femoral component may include: an anteriorjoint surface; a posterior joint surface having a cross-sectional shapedefining a portion of a cylinder, wherein the posterior joint surfaceextends along at least 135 degrees of the cylinder and includes alateral condyle, a medial condyle, and an intercondylar opening disposedbetween the lateral and medial condyles; and medial and lateral groovesextending across the femoral component between the anterior jointsurface and the medial and lateral condyles. The tibial component mayalso include a bone attachment side for attaching to a cut proximal endof a tibia and a joint facing side opposite the bone attachment side.

The meniscal component may include an inferior side for mating with thetibial component, a superior side for mating with the femoral component,an anterior side, a posterior side, a lateral side and a medial side.The meniscal component may also include: an anterior articulatingsurface on the superior side for mating with the anterior joint surfaceof the femoral component; a posterior lateral articulating surface onthe superior side for mating with the lateral condyle of the femoralcomponent, the posterior lateral articulating surface having anapproximately horizontal profile in an anterior-to-posterior direction;a posterior medial articulating surface on the superior side for matingwith the medial condyle of the femoral component, the posterior medialarticulating surface having an upward sloping profile in ananterior-to-posterior direction; medial and lateral projections on thesuperior side for mating with the medial and lateral grooves of thefemoral component; a post extending from the superior surface andconfigured to mate with the intercondylar opening of the femoralcomponent, wherein a central axis of the post is disposed closer to theposterior side than to the anterior side of the meniscal component; andan anterior cutout on the anterior side of the superior surface toprevent injury to a patellar tendon.

In one embodiment, the bone attachment side of the femoral component mayinclude three surfaces for attaching to a three-cut configuration of thedistal end of the femur. In one embodiment, the anterior joint surfaceof the femoral component may include a trochlear groove that is offsetfrom a midline axis of the femoral component in a direction slantingfrom medial to lateral as the groove extends toward an anterior,superior edge of the femoral component. In one embodiment, the post ofthe meniscal component may have an asymmetrical shape in at least twodimensions. For example, in some embodiments, the post may have ahelical twist shape as viewed from a superior aspect. Optionally, ananterior convex surface of the post may conform to an anterior concavesurface of the intercondylar opening of the femoral component, and aposterior convex surface of the post may conform to a posterior concavesurface of the intercondylar opening of the femoral component.Additionally, in some embodiments a posterior portion of the post may bewider than an anterior portion of the post. Also optionally, a superiorsurface of the post may slope downward in a posterior-to-anteriordirection, and the superior surface may have an asymmetric convexconfiguration.

In some embodiments, the anterior cutout on the meniscal component maybe asymmetrically disposed along the anterior side, biased toward thelateral side. Also in some embodiments, the prosthesis may furtherinclude a patellar component having a cutout portion on an inferioredge.

In another aspect of the invention, a meniscal component of a kneeprosthesis for use in a total knee replacement surgical procedure mayinclude: an inferior side for mating with a tibial component of a kneeprosthesis; a superior side for mating with a femoral component of theknee prosthesis; an anterior side, a posterior side, a lateral side anda medial side; a concave anterior articulating surface on the superiorside toward the anterior side for mating with a convex anterior jointsurface of a femoral component; a posterior lateral articulating surfaceon the superior side for mating with a lateral condyle of the femoralcomponent, the posterior lateral articulating surface having anapproximately horizontal profile in an anterior-to-posterior direction;a posterior medial articulating surface on the superior side for matingwith a medial condyle of the femoral component, the posterior medialarticulating surface having an upward sloping profile in ananterior-to-posterior direction; medial and lateral projections on thesuperior side for mating with medial and lateral grooves on the femoralcomponent; a post extending from the superior surface and configured tomate with the intercondylar opening of the femoral component, wherein acentral axis of the post is disposed closer to the posterior side thanto the anterior side of the meniscal component; and an anterior cutouton the anterior side of the superior surface to prevent injury to apatellar tendon. As described above, the post of the meniscal componentmay have an asymmetrical shape in at least two dimensions.

In another aspect of the present invention, a knee prosthesis for use ina total knee replacement surgical procedure may include a femoralcomponent as described above and a meniscal component. The meniscalcomponent may be largely as describe above but may include a boneattachment side for attaching to a cut proximal end of a tibia and asuperior side for mating with the femoral component, thus eliminatingthe need for a separate tibial component. In some embodiments, themeniscal component may be made entirely of a polymer such asultra-high-molecular-weight polyethylene (UHMWPE). As in previouslydescribed embodiments, the prosthesis may optionally also include apatellar component having a cutout portion on an inferior edge.

For a further understanding of the nature and advantages of theinvention, reference should be made to the following description takenin conjunction with the accompanying figures. However, each of thefigures is provided for the purpose of illustration and description onlyand is not intended to limit the scope of the embodiments of the presentinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a perspective view of a knee prosthesis, including femoral,meniscal, tibial and patellar components, in place within a knee joint,according to one embodiment;

FIG. 1B is a perspective view of the knee prosthesis of FIG. 1A, withthe patellar component removed;

FIG. 1C is a perspective view of the knee prosthesis of FIGS. 1A and 1Bwithout the femur or tibia shown;

FIG. 1D is an exploded view of the knee prosthesis of FIGS. 1A-1C;

FIGS. 2A-2E are top, perspective, posterior, medial and anterior views,respectively, of a femoral component of a knee prosthesis, according toone embodiment;

FIG. 2F is a side, diagrammatic view of a femoral component, accordingto one embodiment;

FIG. 2G is a side view of a prior art femoral component of a kneeprosthesis;

FIGS. 2H-2K are posterior comparison views of two femoral components,according to two different embodiments;

FIGS. 3A-3E are top, perspective, medial, anterior and lateral views,respectively, of a meniscal component of a knee prosthesis, according toone embodiment;

FIG. 3F is a top, cross-sectional view of meniscal and femoralcomponents of a knee prosthesis, showing conforming posterior surfacesaccording to one embodiment;

FIG. 3G is a top, cross-sectional view of meniscal and femoralcomponents of a knee prosthesis, showing conforming anterior surfaces,according to one embodiment;

FIG. 3H is a top view of a meniscal component of a knee prosthesis,according to one embodiment;

FIGS. 3I and 3J are a top view of a meniscal component and a side viewof meniscal, femoral and patellar components of a knee prosthesis,respectively, according to one embodiment;

FIG. 3K is a top view of a meniscal component of a knee prosthesis,according to one embodiment;

FIGS. 3L-3N are posterior, medial and lateral views, respectively, of ameniscal component of a knee prosthesis, according to one embodiment;

FIGS. 4A-4D are top, perspective, posterior and side views,respectively, of a tibial component of a knee prosthesis, according toone embodiment.

FIGS. 5A and 5B are anterior and perspective/posterior views,respectively, of a patellar component of a knee prosthesis, according toone embodiment;

FIG. 5C is an anterior view of a prior art patellar component of a kneeprosthesis;

FIGS. 6A-6E are perspective views of femoral and meniscal components ofa knee prosthesis, according to one embodiment, demonstrating how thecomponents move during a range of motion of a knee joint from extensionto flexion as follows: 4 degrees hyperextension (FIG. 6A); 0 degreesflexion (FIG. 6B); 45 degrees flexion (FIG. 6C); 90 degrees flexion(FIG. 6D); and 135 degrees flexion (FIG. 6E);

FIGS. 7A-7E are side views of the femoral and meniscal componentsthrough the same range of motion shown in FIGS. 6A-6E;

FIGS. 8A-8E are posterior views of the femoral and meniscal componentsthrough the same range of motion shown in FIGS. 6A-6E and 7A-7E; and

FIGS. 9A-9E are anterior views of the femoral and meniscal componentsthrough the same range of motion shown in FIGS. 6A-6E, 7A-7E and 8A-8E.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIGS. 1A-1D, in one embodiment, a knee prosthesis system 10may include a femoral component 12, a meniscal component 14, a tibialcomponent 16, and optionally a patellar component 18. In FIG. 1A, kneeprosthesis system 10 is shown with patellar component 18, while in FIGS.1B-1D, it is shown without patellar component 18. In other embodiments,system 10 may be provided without tibial component 16, for example whenmeniscal component 14 attaches directly to the cut tibia (not shown). Inyet other embodiments, multiple sizes of one or more components may beprovided as part of system 10, for example as a kit or suite ofoperating room tools so that a surgeon can select a desired size of eachcomponent or set of components. Generally, therefore, system 10 mayinclude any two or more components of a knee prosthesis as describedherein. Although system 10 is typically described below as includingfemoral 12, meniscal 14 and tibial 16 components, with an optionalpatellar component 18, this description is provided for exemplarypurposes and should not be interpreted to limit the scope of the claims.

FIG. 1A shows knee prosthesis system 10 in place within a knee joint ofa left leg. Here, femoral component 12 is attached to the femur F,tibial component 16 is attached to the tibia T, meniscal component 14 isdisposed between the two, and patellar component is floating in aposition generally located where it would be when attached to a patella(not shown for ease of illustration). The ligaments or tendons of theknee joint are not shown in FIG. 1, so that system 10 may be more easilyseen.

The embodiment of system 10 and components 12, 14, 16, 18 shown in FIG.1A and many of the subsequent figures in this application is configuredfor a left knee. It is described as having a lateral side L and a medialside M, conforming to the lateral and medial sides of the knee,respectively. Of course, in another embodiment, system 10 is provided inmirror image for use on a right knee, and in some embodiments a kit orsystem may include multiple knee prostheses for a left knee and a rightknee or even for multiple sizes of left and right knees. Therefore,although many references will be made to the lateral side L and medialside M of components 12, 14, 16, 18 and system 10, these sides may bereversed in alternative embodiments, and the descriptions thus shouldnot be interpreted as limiting the invention as claimed.

FIG. 1B illustrates knee prosthesis system 10 in place within a kneejoint with patellar component 18 removed. FIG. 1C is a perspective viewof knee prosthesis system 10 by itself, also without patellar component18.

Referring now to FIG. 1D, an exploded view of knee prosthesis system 10helps illustrate further details of femoral component 12, meniscalcomponent 14 and tibial component 16. For example, in the embodimentshown, femoral component 12 includes a bone attachment side 20 and ajoint facing side 22. Bone attachment side 20 has three surfaces atdifferent angled orientations from one another (see FIGS. 2A-2D), toprovide for attachment to a 3-cut distal end of a femur F. In analternative embodiment, bone attachment side 20 may include fivesurfaces, for attachment to a 5-cut distal end of a femur F, or anyother suitable number of surfaces to provide for alternative femoralbone cut configurations. Generally, the 3-cut configuration is used forrevision TKA procedures, while the 5-cut configuration is used fororiginal (or “primary”) TKA procedures. This is not a requirement forthe present application, however, and although the 3-cut bone attachmentside 20 is shown and described herein, system 10 may be used for primaryor revision TKA procedures in various embodiments.

Joint facing side 22 of femoral component 12 may include an anteriorarticulating surface 24, a posterior articulating surface 25 including amedial condyle 25 a and a lateral condyle 25 b, a medial groove 26 a anda lateral groove 26 b between the articulating surfaces 24, 25, anintercondylar opening 28, and a trochlear groove 30 extending verticallyalong anterior articulating surface 24. These and other features offemoral component 12 are described in greater detail below.

Still referring to FIG. 1D, meniscal component 14 may include a post 32for mating with the intercondylar opening 28 of femoral component 12, amedial projection 34 a and a lateral projection 34 b (not visible inthis figure) for mating with lateral grooves 26 a, 26 b of femoralcomponent 12, and an anterior cutout 36 on its anterior/superior sidefor preventing injury to the patellar tendon. These and other featuresof meniscal component 14 are described in greater detail below.

Tibial component 16 includes a joint facing side 40, a bone attachmentside 38, and a bone attachment stem 43 for extending into the tibia tofacilitate bone attachment. Tibial component 16 is also described ingreater detail below.

All components 12, 14, 16, 18 of knee prosthesis system 10 may be madeof any suitable material for manufacturing knee prostheses. For example,in some embodiments, femoral component 12 and tibial component 16 may bemade of a metal, while meniscal component 14 and patellar component 18may be made of a polymer. In other embodiments, tibial component 16 mayalso be made of a polymer. In some embodiments, one of more of thecomponents may be made of ceramic. Knee prosthesis system 10, therefore,may incorporate any suitable material(s) and combinations thereof.Typical implant metals include CoCr (Cobalt-Chrome), and Ti-6Al-4V(Titanium Alloy). A typical polymer is UHMWPE (Ultra-High MolecularWeight Polyethylene). Ceramics include Zirconia, Zirconia-ToughenedAlumina (ZTA), Alumina, and oxidized zirconium (metal-ceramic). Someimplants may also be coated (or part of an implant may be coated) withany of a number of suitable coating materials. For example, somecoatings are used on implants to increase bone-cement-implant adhesionand promote ingrowth. Potential coatings include HA (Hydroxyapatite),TPS (Titanium Plasma Spray), RBM (Resorbable blast media) and porousCcoatings (spherical beads, asymmetrical powder and irregular particlecoatings).

Components 12, 14, 16, 18 of knee prosthesis system 10 may also beprovided in any suitable size, combinations of sizes, kits includingmultiple sizes, or the like. For example, in one embodiment, femoralcomponent 12 may have any of a number of different distal thicknesses(or “heights”) while maintaining the distal profile, posterior thicknessand anterior thickness of joint facing surface 22. These femoralcomponents 12 of multiple thicknesses may be provided to allow a surgeonto select a desired thickness without needing to use augments oroffsets. One example of such a kit of different distal thicknesses of afemoral component is described in U.S. Pat. No. 7,837,737, thedisclosure of which is hereby incorporated by reference. Thus, kneeprosthesis system 10 is not dependent on sizes of components and may beprovided in any suitable size or combination of sizes as desired.

FIGS. 2A-2E show femoral component 12 in greater detail. FIG. 2A, a topview, shows the three surfaces 20 a, 20 b and 20 c of this embodiment ofbone attachment side 20, a bone attachment member 27, ananterior/superior edge 21, a posterior/superior edge 23, andintercondylar opening 28, which has an anterior surface 28 a and aposterior surface 28 b. This view also shows that anterior joint surface24 is asymmetric, slanting toward the lateral side L toward theanterior/superior edge 21. Bone attachment member 27 may have any of anumber of suitable configurations and may include a post, as shown.Ideally, bone attachment member 27 is made as small as possible whilealso helping provide secure attachment to the femur, so that as small afemoral cut as possible may be made.

The shape and location of intercondylar opening 28 and its anterior 28 aand posterior 28 b surfaces are configured for mating with post 32 onmeniscal member 14. Surfaces 28 a, 28 b may be regarded as cam surfaces,which interact with corresponding anterior and posterior surfaces ofpost 32 during rotation of the knee joint. Posterior cam surface 28 bproduces rollback in the form of posterior translation of the femurrelative to the tibia as it rides against meniscal component post 32.Anterior cam surface 28 a is used to stabilize femoral component 12 withmeniscal component 14 in full extension.

Shape of intercondylar opening 28 is designed to conform closely to theshape of post 32, so that the two parts conform to one another duringmovement to enhance stability while still allowing for a full range ofmotion.

Referring now to FIG. 2B, a perspective view of femoral component 12,trochlear groove 30 on anterior surface 24 is shown in greater detail,as are medial groove 26 a and lateral groove 26 b. The asymmetry ofanterior surface 24 is also demonstrated in this figure. As mentionedabove, anterior articulating surface 24 of femoral component 12 isasymmetrically slanted toward the lateral side of femoral component 12toward its anterior/superior edge 21. Trochlear groove 30 is also offsetlaterally. In other words, instead of traveling vertically up anteriorarticulating surface 24, trochlear groove 30 angles toward the lateralside in the anterior/superior direction. This offset configuration oftrochlear groove 30 improves patellar tracking.

Medial and lateral grooves 26 a, 26 b divide femoral component 12 intoanterior and posterior articulating surfaces 24, 25, the latter havingtwo parts-medial condyle 25 a and lateral condyle 25 b. Together withprotrusions 34 a, 34 b of meniscal component 14, grooves 26 a. 26 b helpprovide knee prosthesis 10 with anterior-posterior stability, helpreduce paradoxical shift/translation of the knee, and enhancepatellofemoral tracking when implanted in a knee joint.

FIG. 2C is a posterior view of femoral component 12. From thisviewpoint, intercondylar opening 28 and its anterior surface 28 a arevisible. Also, the cylindrical shape of posterior articulating surface25 is evident. This cylindrical shape is discussed further below, and analternative embodiment is discussed in relation to FIG. 3A.

In FIGS. 2D and 2F, medial side views, the cylindrical shape ofposterior articulating surface 25 is again shown. As the knee rotatesthrough its range of motion from extension to flexion and back toextension, the tibia rotates about the femur around an axis of rotationA (FIG. 2F). Posterior articulating surface 25, including medial condyle25 a and lateral condyle 25 b, are the portion of femoral component 12about which the majority of this rotation occurs. Posterior articulatingsurface 25 may thus be said to have an axis of rotation A about whichthe cylindrical shape of surface 25 is formed. This cylinder may be saidto have a radius R from axis A to posterior surface 25, One of theadvantageous features of femoral component 12 is that posterior jointsurface 25 conforms to the radius R of the cylinder drawn about the axisof rotation A for at least about 120 degrees, and more preferably atleast about 135 degrees, and even more preferably about 180 degrees ormore. This configuration of posterior articulating surface 25 may bereferred to as a “cylindrical radius,” which ends in grooves 26 a, 26 b.By contrast, and referring to FIG. 2G, currently available femoralcomponents of knee prosthesis generally have a posterior portion thatconforms to the radius of a cylinder for only 90 degrees at most. Theposterior shapes of these currently available devices then move awayfrom the radius. The advantage of having posterior surface 25 thatconforms to the radius of the cylinder for at least 120 degrees (andpreferably closer to or equal to 180 degrees) is that, along withgrooves 26 a, 26 b, this feature enhances stability and the naturalkinematics (motion) of the knee. Tests have shown that this shapeprovides a more natural knee movement.

Still referring to FIGS. 2D and 2F, femoral component 12 may also bedescribed as having an anterior radius of curvature involving anteriorarticulating surface 24 and a posterior radius of curvature R involvingposterior articulating surface 25. Posterior radius of curvature R wasjust described and involves the tibiofemoral portion of the knee joint.The anterior radius of curvature refers to the radius of rotation of thepatella about the femur (or femoral component 12)—i.e., thepatellofemoral joint. The anterior and posterior curvatures intersect atthe location of grooves 26 a and 26 b.

FIG. 2E is an anterior/superior view of femoral component 12, againdemonstrating the asymmetrical shape of anterior articulating surface 24and trochlear groove 30. As mentioned previously, this asymmetry isreversed in a knee prosthesis configured for the opposite (right) knee.

Referring now to FIGS. 211 and 21, an alternative embodiment of femoralcomponent 12 is explained. FIG. 2H is a posterior view of the previouslydescribed embodiment of femoral component 12 and meniscal component 14with post 32. Femoral component 12 has medial 25 a and lateral 25 bcondyles, which have a generally cylindrical overall shape, andintercondylar opening 28 between the two. In an alternative embodiment,however, as shown in FIG. 2I, a femoral component 112 may have anintercondylar opening 128 and a medial condyle 125 a and a lateralcondyle 125 b that conform to more of a spherical shape. In thisembodiment, meniscal component 114 also has a more concave shape to matewith the spherical shape of femoral component 112. In alternativeembodiments, either of these configurations of femoral component 12, 112and meniscal component 14, 114 may be used.

Referring now to FIGS. 3A-3E, meniscal component 14 is shown in greaterdetail. Meniscal component 14 may be described as having a superior side50 for mating with femoral component 12, an inferior side 52 for matingwith tibial component 16, an anterior side 54, a lateral side 56, amedial side 58 and a posterior side 60. On superior side 50, asmentioned previously, meniscal component 14 includes posteriorstabilization post 32, medial protrusion 34 a for mating with medialgroove 26 a of femoral component, lateral protrusion 34 b for matingwith lateral groove 26 b of femoral component, and anterior cutout 36for preventing injury to a patellar tendon. Superior side 50 may alsoinclude an anterior articulating surface 62 for mating with anteriorjoint surface 24 of femoral component 12, a posterior medialarticulating surface 64 a for mating with medial condyle 25 a of femoralcomponent 12, and a posterior lateral articulating surface 64 b formating with lateral condyle 25 b of femoral component 12.

As shown in FIG. 3A (a top view of meniscal component 14), post 32 maybe described as having an anterior surface 66 a and a posterior surface66 b. These surfaces 66 a, 66 b interact with anterior cam surface 28 aand posterior cam surface 28 b of intercondylar opening 28 of femoralcomponent 12. Compared to currently available knee prostheses, post 32is located farther toward posterior side 60 of meniscal component 14.For example, a central axis drawn vertically through approximately thecenter of post 32 is located closer to posterior side 60 than toanterior side 54. In one embodiment, post 32 is located approximatelyone third of the total anterior/posterior distance from posterior side60. The advantages of this more posterior location of post 32 mayinclude: (1) It better replicates natural knee motion/kinematics byallowing for greater rollback of the tibia over the femur; (2) Byplacing the post more posterior, and having a cylindrical radius with acenter that is close to the insertion point of the PCL, this designengages the posterior stabilizer earlier and transitions easily fromrotation to posterior “rollback” at the correct time to replicatenatural kinematics; (3) It makes posterior surface 66 b of post 32engage with posterior cam surface 28 b of femoral component 12 earlierin flexion (i.e., at a smaller angle of flexion, such as about 20degrees instead of about 45 degrees with conventional prostheses), whichincreases stability; (4) It increases the range of motion about theknee; and (5) It allows less bone removal from the distal femur duringthe surgical procedure.

Referring now to FIGS. 3A and 3F, in at least one embodiment, posteriorstabilization post 32 has a shape that conforms in multiple differentways to intercondylar opening 28 of femoral component 12. Post 32 isalso asymmetrical in multiple ways. For example, as illustrated by FIGS.3A and 3F, post 32 may have a slight helical twist from a top down view(in a counterclockwise direction in the figure). The helical twist shapemay allow posterior cam surface 28 b of femoral component 12 to betterconform to posterior surface 66 b of post during the range of motion ofthe knee and especially during internal tibial rotation, which mayreduce wear and tear on post 32. The twist shape may also helpfacilitate natural knee kinematics by encouraging posterior translationof lateral condyle 25 b and pivoting of medial condyle 25 a duringflexion (illustrated by curved arrow in FIG. 3F).

With reference to FIGS. 3A and 3G, anterior surface 66 a of post 32 mayalso have a shape that conforms to anterior cam surface 28 a ofintercondylar opening 28. This conformity of the corresponding surfaceshelps stabilize the knee when returning from flexion to extension orwhen simply in a state of extension or low flexion. The conformity ofthe surfaces also reduces peak stresses on anterior cam surface 66 a,reducing potential for wear and premature fatigue.

Referring to FIGS. 3A and 3H, post 32 may also have a tapered profile,looking from a top down view, going from a wider profile posteriorly toa narrower profile anteriorly. This tapered profile may be produced bymaking an angular cut down the medial side of post 32, thus creatinganother asymmetry. Again, this asymmetry helps facilitate internaltibial rotation during flexion of the knee. The tapered profilemaintains prosthesis constraint/stability between post 32 andintercondylar opening 28 in early flexion and extension, while allowinginternal tibial rotation at higher flexion angles in the kinematic rangeof motion.

Turning now to FIGS. 3B, 3I and 3J, post 32 may also include a slopedanterior/superior surface 68 with a small, asymmetric concavity (or“cutout”). The concavity generally has a tapered posterior-to-anteriorprofile. As illustrated by FIG. 33, the slope and especially theasymmetric concavity of anterior/superior surface 68 are configured toreduce contact with patellar component 18 as the knee moves into deepflexion. This reduced contact, in turn, reduces wear and tear on post 32and patellar component 18.

Referring to FIGS. 3A, 3B and 3K, meniscal component 14 may also includean asymmetric anterior cutout 36 at the juncture of superior side 50 andanterior side 54. Cutout 36 is configured to minimize tenting of thepatellar tendon over the meniscal component 14 as the knee flexes.Relief 36 also reduces the risk of patellar component 18 contacting themeniscal component 14 in situations in which the joint line has moved,either purposefully or as an unintended effect of the surgicalprocedure, proximally and anteriorly. As best seen in FIG. 3K,anterior/superior cutout 36 is positioned asymmetrically, closer tolateral side 56, to compensate for internal rotation of the tibiarelative to the femur during flexion.

Referring to FIGS. 3C (medial side view), 3E (lateral side view), 3L(posterior view), 3M (medial cross-section), and 3N (lateralcross-section), meniscal component 14 may include yet another feature toenhance the kinematics of a knee in which knee prosthesis system 10 isimplanted. FIG. 3L shows that the superior edge of posterior medialarticulating surface 64 a is higher than the superior edge of posteriorlateral articulating surface 64 b. In other words, posterior side 60 hasa height H1 at the medial side that is greater than its height H2 at thelateral side. This is due to the fact that, in this embodiment,posterior medial articulating surface 64 a has an upward slope or slamin an anterior-to-posterior direction, while posterior lateralarticulation surface 64 b has an approximately horizontal (or “flat”)profile in an anterior-to-posterior direction. The difference betweenthe two posterior articulating surfaces is best shown in FIGS. 3M(medial sloping surface 64 a) and 3N (lateral horizontal surface 64 b).These surfaces 64 a, 64 b are also shown in FIGS. 3C and 3E. In theembodiment shown, for example, the upward slope angle of medialarticulating surface 64 a is approximately 3 degrees, and the profileangle of the posterior articulating surface 64 b is approximately 0degrees. In alternative embodiments, slight changes to these angles maybe made. For example, in one alternative embodiment, medial articulatingsurface 64 a may have a slightly larger slope such as between about 4degrees and about 5 degrees, and posterior articulating surface 64 b mayhave a slight slope such as between about 1 degree and about 2 degrees.Thus, although the 3-degree/0-degree combination has been shown in teststo provide natural knee kinematics, other combinations might bepossible. This configuration of medial articulating surface 64 a andposterior articulating surface 64 b is another feature that helpsreplicate natural knee kinematics in knee prosthesis 10 by helping keepmedial condyle 25 a of femoral component 12 in place while allowinglateral condyle 25 b to translate posteriorly relative to meniscalcomponent 14. Again, this facilitates tibial rotation and posteriortranslation during flexion.

Turning now to FIGS. 4A-4D, tibial component 16 according to oneembodiment is shown in greater detail. In this embodiment, tibialcomponent 16 generally includes a joint facing surface 40 for matingwith meniscal component 14, a bone attachment surface 38, one or moreattachment features 41 for attaching to meniscal component 14, andanterior 55, posterior 61, medial 57 and lateral 59 sides. Tibialcomponent may also include a post 43 for extending into the tibia toenhance attachment to the bone. According to various embodiments, tibialcomponent 16 may have any of a number of suitable sizes and shapes toattach to tibial bone and to meniscal component 14, and thus theembodiment shown is only one example. Tibial component may be made ofany suitable material, typically but not necessarily metal or polymer.

Referring now to FIGS. 5A and 5B, patellar component 18 is shown ingreater detail. Patellar component 18 may have any suitable shape(domed, symmetric, asymmetric, etc.) and may include an inferior relief42 (or “cutout”). In contrast, traditional patellar components have acircular anterior-view profile (FIG. 7C). Relief 42 reduces the risk ofpatellar component 18 contacting the meniscal component 14 duringmid-to-deep flexion in situations (known as patella baja) in which thejoint line has moved, either purposefully or as an unintended effect ofthe surgical procedure, proximally and anteriorly.

FIGS. 6-9 illustrate femoral component 12 and meniscal component 14 invarious stages of motion of a knee through a range of motion fromextension to flexion, to show how these two components 12, 14 interactwith one another to facilitate natural knee kinematics. In each set offigures, the first figure (the “A” figure) shows components 12, 14 in 4degrees of hyperextension, the second figure (the “B” figure) showscomponents 12, 14 in 0 degrees of flexion, the third figure (the “C”figure) shows components 12, 14 in 45 degrees of flexion, the fourthfigure (the “D” Figure) shows components 12, 14 in 90 degrees offlexion,and the fifth figure (the “E” figure) shows components 12, 14 in 135degrees offlexion. FIGS. 6A-6E are perspective views, FIGS. 7A-7E aremedial side views, FIGS. 8A-8E are posterior views, and FIGS. 9A-9E arefront views.

With the knee in 4 degrees of extension (i.e., maximal or hyperextension) (FIGS. 6A, 7A, 8A, 9A), protrusions 34 a, 34 b on meniscalcomponent 14 mate with grooves 26 a, 26 b on femoral component 12 toprovide stability to the joint by limiting rotation and anteriortranslation of femoral component 12 relative to meniscal component 14.Preventing such translation makes the patient's knee feel more stableand thus more natural. Additionally, the anterior side of protrusions 34a and 34 b restricts posterior translation of the femoral component 12relative to meniscal component 14, which prevents blunt impact andexcessive forces and wear on the anterior cam surface 28 a. Protrusions34 a, 34 b may alternatively be referred to as a “wave.” In alternativeembodiments, protrusions 34 a, 34 b may be replaced with one protrusionthat extends all the way across meniscal component 14 and/or grooves 26a, 26 b may be replaced with one groove that extends all the way acrossfemoral component 12.

Referring to FIGS. 6B, 7B, 8B and 9B, when the knee is in 0 degrees offlexion, protrusions 34 a, 34 b and grooves 26 a, 26 b still providestability to the knee. At this point anterior cam surface 28 a ofintercondylar opening 28 contacts anterior surface 66 a of post 32. Thiscontact provides additional anterior-posterior stability and positionscomponents 12, 14 relative to one another.

FIGS. 6C, 7C, 8C and 9C show components 12, 14 as if attached to a kneein 45 degrees of flexion. At this stage, which might be referred to as“mid-flexion,” the tibia (and meniscal component 14) rotates internallyrelative to the femur (and femoral component 12). In other words, in theleft knee (as in the figures), the tibia rotates clockwise in a top viewrelative to the femur as the knee flexes. In the right knee, the tibiarotates counterclockwise in top view in flexion. Also at this stage,posterior cam surface 28 b of intercondylar opening 28 contactsposterior surface 66 b of post 32. This contact begins to turn rotarymotion of the two components 12, 14 into posterior translation of thelateral condyle 25 b of femoral component 12 relative to meniscalcomponent 14.

With the knee in 90 degrees of flexion, as in FIGS. 6D, 7D, 8D and 9D,posterior cam surface 28 b slides down posterior surface 66 b of post 32and creates posterior translation and internal rotation of meniscalcomponent 12 relative to femoral component 14. This rotation isillustrated well by FIG. 7D. Contact of posterior cam surface 28 b withposterior surface 66 b drives both condyles 25 a, 25 b in the posteriordirection, but lateral condyle 25 b translate posteriorly farther thanmedial condyle 25 a.

In deep flexion (135 degrees), as in FIGS. 6E, 7E, 8E and 9E, therotation of femoral component 12 relative to meniscal component 14 iseven more pronounced. This is shown best in FIG. 7E. The reverse ofthese motions of components 12, 14 occurs when the knee is moved fromflexion to extension.

1. A knee prosthesis for use in a total knee replacement surgicalprocedure, the knee prosthesis comprising: a femoral componentcomprising: a bone attachment side for attaching to a cut distal end ofa femur; a joint facing side opposite the bone attachment sidecomprising: an anterior joint surface; a posterior joint surface havinga cross-sectional shape defining a portion of a cylinder, wherein theposterior joint surface extends along at least 135 degrees of thecylinder and comprises: a lateral condyle; a medial condyle; and anintercondylar opening disposed between the lateral and medial condyles;and medial and lateral grooves extending across the femoral componentbetween the anterior joint surface and the medial and lateral condyles;a tibial component comprising:  a bone attachment side for attaching toa cut proximal end of a tibia; and  a joint facing side opposite thebone attachment side; and  a meniscal component, having an inferior sidefor mating with the tibial component, a superior side for mating withthe femoral component, an anterior side, a posterior side, a lateralside and a medial side, the meniscal component further comprising:  ananterior articulating surface on the superior side for mating with theanterior joint surface of the femoral component;  a posterior lateralarticulating surface on the superior side for mating with the lateralcondyle of the femoral component, the posterior lateral articulatingsurface having an approximately horizontal profile in ananterior-to-posterior direction;  a posterior medial articulatingsurface on the superior side for mating with the medial condyle of thefemoral component, the posterior medial articulating surface having anupward sloping profile in an anterior-to-posterior direction;  medialand lateral projections on the superior side for mating with the medialand lateral grooves of the femoral component;  a post extending from thesuperior surface and configured to mate with the intercondylar openingof the femoral component, wherein a central axis of the post is disposedcloser to the posterior side than to the anterior side of the meniscalcomponent; and  an anterior cutout on the anterior side of the superiorsurface to prevent injury to a patellar tendon.